Conventionally, a gas sensor is used for detecting the concentration of a particular component (oxygen, etc.) in exhaust gas from an internal combustion engine. The gas sensor has a gas sensor element therein. The gas sensor element is composed of a cell having a solid electrolyte member and a pair of electrodes disposed on the solid electrolyte member, etc. The gas sensor externally has a threaded portion and is mounted to a mount body (exhaust pipe, etc.) by means of the threaded portion being threadingly engaged with a mounting hole formed in the mount body.
Usually, after the gas sensor is mounted to an exhaust pipe, a connector connected to the lead wires extending from the gas sensor is connected to a connector of an external circuit or the like. However, in the case where the gas sensor and the external circuit are united without use of connectors or where the connector is to be fixed before the gas sensor is fixed, difficulty is encountered in threadingly engaging the gas sensor with the mounting hole, since the external circuit and the lead wires must be rotated together with the gas sensor.
In order to cope with such difficulty, there has been disclosed a technique in which a tubular rotary member is disposed in such a manner as to surround a metallic shell (housing) which holds a gas sensor element; is rotatable relative to the metallic shell; and has a threaded portion on its outer circumferential surface (refer to Patent Documents 1 and 2). By virtue of such a configuration, even when the gas sensor and the external circuit are united, the gas sensor can be threadingly engaged with the mounting hole without need to rotate the external circuit together therewith.